1. Filed of the Invention
This invention relates to ohmic connection electrodes for p-type semiconductor diamonds.
2. Description of the Prior Art
The semiconductor diamond is now drawing industrial attention as a new material for semiconductor devices such as diodes, transistors, sensors, or the like.
Although the diamond is widely known as an insulating substance, the one discussed herein is a semiconductor diamond having low resistivity.
The diamond has broad forbidden band width (5.5 eV) as well as a large mobility of carriers (2000 cm.sup.2 /Vs), and is stable thermally and chemically.
For these reasons, the semiconductor diamond is keenly expected as a material for environmentally withstanding, high-speed power-use devices or blue light emitting elements.
The semiconductor diamond is available in the forms of a natural bulk, high-pressure synthetic bulk, and vapor-phase synthetic film.
The p-type diamond can be obtained by doping boron (B).
On the other hand, the n-type diamond, though it may be obtained by doping phosphorus (P) and lithium (Li), has a high resistivity. And an n-type diamond with a low resistivity has not yet been developed.
Although bipolar devices are not involved, the devices that have already come out in prototypes on the basis of the semiconductor diamond include at present Schottky diodes, making use of Schottky junction with tungsten (W) and a p-type diamond, and several types of unipolar transistors.
In manufacturing semiconductor devices, it is extremely important to form such electrodes that allow ohmic connection. The ohmic connection electrode is an electrode with current-voltage characteristics which are symmetric between the forward and backward directions in accordance with the Ohm's law. Moreover, it is preferable that the contact resistance thereof be as low as possible, where the contact resistance is defined as a voltage applied to make a unit current flow through a unit contact surface. The unit thereof is .OMEGA.cm.sup.2.
It is common knowledge that an electrode capable of ohmic connection can be obtained by forming some metals such as Ti, AuTi, and AuTa through the method of metallizing on a p-type diamond.
The technique of forming ohmic connections is an important technique in manufacturing semiconductor devices.
However, the ohmic connections now available to semiconductor diamonds using Ti, AuTa, and the like involve a large contact resistance as much as more than 1 .OMEGA.cm.sup.2.
In any device manufactured using the conventional ohmic connection with the semiconductor diamond, even if a voltage is applied to it, there occurs a remarkable voltage drop across such an ohmic connection electrode. This results in a drop of an effective voltage applied to the device, whereby good characteristics of the semiconductor diamond connection can not be sufficiently utilized. Furthermore, the device suffers from a serious drawback that heat is generated at an ohmic connection electrode.
In manufacturing any electronic devices, contact resistances less than 10.sup.-4 .OMEGA.cm.sup.2 are required for that of ohmic connections, and far lower contact resistances are demanded for high-speed, high-frequency devices.
To enable the semiconductor diamond to be utilized as a material for semiconductor devices, a low-resistance ohmic connection is essential.